Manually operable switch with liquid operating medium

ABSTRACT

A manually operable switch in which the operating force is dissipated after operation so that the switch is restored to an unoperated condition from which it is again capable of operation, notwithstanding the pressure which generated the operating force continues to be applied to the switch.

United States Patent [191 Lusti et al.

[ MANUALLY OPERABLE SWITCH WITH LIQUID OPERATING MEDIUM [75] Inventors: John Lusti, River Vale, N.J.; Sergius Paul Krzyzanowski, Flushing, NY.

[73] Assignee: Otis Elevator Company, New York,

22 Filed: July 23,1973

[21] Appl. No.: 382,239

[52] US. Cl. 200/160, 200/83 T, 200/83 W, 200/83 Z [51] Int. Cl. H0lh 13/50 [58] Fieldof Search 200/160, 34, 83 T, 83 W,

[56] References Cited UNITED STATES PATENTS 1,059,013 4/1913 Urgnhart 200/160 Jan. 21, 1975 2,794,868 6/1957 McMorran et a1 200/34 2,800,538 7/1957 Kuhn 200/160 2,866,862 12/1958 Bachi 200/34 3,185,180 5/1965 Fish et a1. 200/81 3,261,958 7/1966 Bittner..... 200/160 3,428,768 2/1969 Golden et 200/83 Primary ExaminerRobert K. Schaefer Assistant ExaminerWilliam J. Smith Attorney, Agent, or Firm-Joseph L. Sharon; Robert T. Mayer [5 7] ABSTRACT A manually operable switch in which the operating force is dissipated after operation so that the switch is restored to an unoperated condition from which it is again capable of operation, notwithstanding the pressure which generated the operating force continues to I be applied to the switch.

11 Claims, 5 Drawing Figures Patented Jan. 21, 1975 FIG. 2'

MANUALLY OPERABLE SWITCH WITH LIQUID OPERATING MEDIUM This invention relates to manuallyoperable switches for electrical circuits.

It is desirable to produce an improved manually operable switch, particularly one which appears to those operating it to be responding to their mere touch. Such a switch possesses aesthetic values as well as having a certain mysterious quality about it which also adds to its appeal. At the same time, of course, it should not be expensive.

It is, therefore, an object of this invention to provide a relatively inexpensive, seemingly touch responsive, manually operable electrical switch. 7

Where manually operable switches are subjected to operation by public, it is common for certain members thereof, be they pranksters or vandals, to tamper with the switches. These people typically do not seek to destroy the switches entirely. Rather, they jam them with pins or gum or tape or some other foreign substances, thereby rendering them temporarily incapable of being operated byothers.

It is another object of this invention to provide a seemingly touch responsive, manually operable switch which is virtually tamper proof.

In a preferred embodiment of the manually operable that means transmits a temporary operating force gen-.

erated by said pressure to the movable contact so as to move that contact in opposition to the spring force from the closed position to anopen one in which it is out of engagement with the fixed contact. Upon the operation of the switch in this manner, the temporary operating force dissipates sufficiently to enable the spring force to restore the movable contact to the closed position even though the predetermined amount of pressure remains applied to the operating member. In this way, the switch is again ready for operation and will respond to additional pressure applied at an effective rate.

The operating member of the preferred embodiment of the switch is a flexible diaphragm which forms one wall of the switch housing. The force transmitting means includes a separator in a hollow cylindrical portion of the switch housing which divides that portion into two separate chambers, the flexible diaphragm forming one wall of one of thesecharnbers. Also included as part of the force transmitting means is a liquid which substantially fills both of these chambers. The separator includes'an aperture which permits the liquid to flow from one chamber to the other. The movable contact is disposed in its closed position to close this aperture substantially. Upon inward flexure of the diaphragm, liquid is caused to flow from one chamber to the other which moves the movable contact from its closed position to its open position.

switch of this invention, a switch housing is provided Other objects, advantages and features of the invention will be evident from the following description when considered in conjunction with the appended claims and accompanying drawing. In the drawing:

FIG. 1 is an exploded view of major elements of the presently preferred embodiment of the invention;

FIG. 2 is a sectional view of the embodiment of FIG. 1 with the elements thereof assembled in the intended manner; 4

FIG. 3 is a sectional view of the embodiment of FIG. 2 taken along lines 3-3;

FIG. 4 is an exploded view of major elements of an alternate embodiment of the invention; and

FIG. 5 is a schematic plan view of major elements of another alternate embodiment of the invention.

Referring now primarily to FIG. 1, switch housing 11 is shown which may be fabricated of any suitable high impact thermoplastic material. In the presently preferred constructed embodiment, Merlon type 2100, color 1045, of the Mobay Chemical Company has been suitably used, although any suitable material would be satisfactory. Housing 11 includes hollowcylindrical portion 12, one end of which is sealed by flexible diaphragm 13 (FIG. 2) which is disposed in a shallow depression formed by raised circular lip 14. Diaphragm 13 is dimensioned to be wide enough and thin enough to yield in asuitably desirable manner upon the application of pressure thereto. In the previously mentioned constructed embodiment, a round diaphragmwith a diameter of 0.95 inches and a thickness of 0.05 inches has been suitably employed.

Fitted snugly into hollow cylindrical portion 12 is separator 15. This element is a molded plastic disc with a concave conical surface adjacent diaphragm 13. This surface in the constructed embodiment has a maximum depth of 0.06 inches. Separator 15 also has formed therein a rectangular aperture 16 that opens into a circular aperture l7.'On each side of rectangular aperture 16 is a contact pin 18a or 18b, each of which possesses a leg portion that extends through a respective hole in separator 15. Each contact pin 18 also includes a foot-v like projection'20a or 20b that projects into rectangular punched. In the constructed embodiment, reed 2l is made of a gold plated, 0.003 inch thick beryllium copper strip. The raised portion is defined by folding sections of the strip downwardly along a line starting at the center of the raised portion end and terminating at the respective edgesone-third of the length of the strip from the raised portion end as illustrated in an exaggerated manner in the drawing. At the raised portion end, the edges of the folded sections in a side view form a angle .with each other.

Reed 21 and pin 18b comprise the movable contact of an electrical contact pair with pin 18a forming the stationary contact. Raised portion 22 defines the contacting surface of the movablecontact which is normally in engagement with the undersurface of foot-like the inside surface of diaphragm 13 and the adjoining concave conical surface of separator 15 define a front or operating chamber A for the switch. A second or dissipating chamber B is defined by reed 21 together with circular aperture 17 and elastomer seal 23. This seal, which rubber in the constructed embodiment, has two holes provided init and is slipped over the leg portions of contact pins 18a and 18b. Cap 24 with its circular ridges 25 and 26 pressed down into seal 23 provide the latter with its gasket-like quality. Cap 24 is held in this position by heat softening segment C (FIG. 2) of the circular wall of cylindrical portion 12 above cap 24 and molding it down over the edge of the cap in any suitable manner. A bulge space 27, with an air hole 28, for seal 23 to expand outwardly into is provided behind seal 23 by the valley in cap 24 surrounded by raised ridge 26. a

In the presently preferred constructed embodiment both the operating or first chamber A and the dissipating or second chamber B are filled with dimethylpolysiloxane at 12,500centistokes. Bleed ports 31 andv 32 (FIG. 3) are formed by the space between the walls on the long sides of rectangular aperture 16 and the cooperating edges of reed 21 which is made sufficiently narrow with respect to the width of aperture 16 to provide the ports. These bleed ports are dimensioned in relation to the fluid which fills chambers A and B to permit that fluid to flow slowly from one chamber to the other through the bleed ports .in response to changes in ambient conditions without affecting the normally closed condition between the contact pair. In

the preferred embodiment these ports each measure 0.5 inches by 0.005 inches.

The foregoing arrangement provides a manually operable switch which seemingly operates in response to the mere touch of a person. When the finger of a person is inserted into the depression formed by lip 14 and pressed lightly against the outer surface of the diaphragm, a light pressure is applied to diaphragm 13 and it flexes inwardly. In the preferred embodiment this flexure generates a temporary operating force for the switch which causes liquid to flow from chamber A to chamber B through rectangular aperture 16 due to the greater fluid pressure in chamber A. In so flowing, the liquidmoves reed 21 upwardly as shown in exaggerated manner in FIG. 2 against its opposing spring force from its normally closed position in which it is in engagement with fixed or stationary contact 18a to an open position out of engagement with that contact until the opposing spring force balances the operating force on reed 21.

To be able to accept the liquid forced out of actuating chamber A, dissipating chamber B must expand its volume. This is accomplished by seal 23'expanding outwardly into bulge space 27 provided by cap 24. Upon expanding sufficiently to receive all the liquid forced out of chamber A" by the inward flexure of diaphragm 13, the operating force generated by that flexure is dissipated because the pressure differential between the chambers is eliminated. Consequently, reed 21 returns in response to its spring force to its closed position in engagement with stationary contact 18a notwithstanding diaphragm 13 remains inwardly flexed the amount which caused the initial opening of the contacts. Return movement of reed 21 under these circumstances, it is to be understood, is dampened by the viscosity of the liquid. The restoration of the switch to its unactuated condition enables it to be operated again with diaphragm 13 remaining inwardly flexed provided the diaphragm is capable of being further inwardly flexed in response to the application of additional pressure thereon.

Should reed 21 return to its closed position before the removal of operating pressure from diaphragm 13, bleed ports 31 and 32 allow for the return flow of liquid from dissipating chamber B to actuating chamber A after the removal of the operating pressure. If, as would probably be the more normal situation, operating pressure is removed from diaphragm 13 before reed 21 returns to engagement with contact 18a, the return flow of liquid would be through the gap provided between reed 21 and contact 18a as well as through bleed ports 31 and 32. On various examples of the disclosed constructed embodiment, a force of 1 oz. applied at the. center of diaphragm 13 produces a flexure between 0.00025 and 0.001 of an inch at that center. When this deflection is produced rapidly enough, it consistently results in operation of the switch. It is to be understood, however, that if the deflection does not occur with sufficient rapidity, all of the liquid displaced thereby flows into back chamber B through bleed ports 31 and 32 without ever moving reed 21 out of engagement with contact 18a. It has been found that while this can be accomplished with the constructed embodiment by a person applying pressure to diaphragm 13 with his finger without mechanical assistance, it takes extreme care and concentration, as well as a high degree of manual control, to do it; and, even then, it cannot be done consistently. In contrast, in normal use of the switch, one typically touches diaphragm 13 with sufficient impact to apply enough force to it rapidly enough to operate the switch without being aware that he has applied any force to it at all. Notwithstanding that one must apply sufficient pressure to diaphragm 13 at an effective rate, one which enables the liquid to flow from chamber A to chamber B at a rapidly enough rate to separate the contacts, the pressure and rate of application required are so slight that the switch, as intended, seemingly operates in response to the mere touch of individuals operating it.

It should also be apparent that the herein disclosed switch is for all intents and purposes tamperproof to the point of destruction. It is not subject to jamming since its movable contact always returns to its unactuated state. Consequently, short of breaking diaphragm 13, abusing it sufficiently even to warp it, does not render the switch inoperable.

One of the advantages of the herein disclosed switch is that none of the dimensions or other parameters of any of the elements need to be maintained within very close tolerances. The extremely low ideal operating force of 1 oz. together with the relatively high viscosity of the liquid employed, for example, permits manufacturing imperfections to increase the size of bleed ports 31 and 32 and the thickness of diaphragm 13 without conspicuously increasing the force needed to be applied to diaphragm 13 to cause the switch to operate. Similarly, the spring force of reed 21 can also be increased without conspicuously increasing the necessary operating force. Also, the ability of the movable contact to return to its unactuated condition, notwithstanding diaphragm 13 remains flexed inwardly, permits the diaphragm to be warped or otherwise misshapen after manufacture without rendering the switch inoperable.

Other arrangements for accomplishing the same result as the presently preferred constructed embodiment have been envisaged. FIGS. 4 and 5 disclose such arrangements. In the FIG. 4 embodiment, actuator 50 is mounted in a housing (not shown) to have its pointed end 59 in engagement with a diaphragm 57 corresponding to diaphragm 13. Actuator S is connected to operating arm 51 through spring 52, which is confined in slot 53. Movable contact arm 54, upon which movable contact 54a is mounted, is similarly connected to actuator 50 by spring 55 which is confined in slot 56. Movable contact 54a normally engages fixed contact 58 which may be mounted in the switch housing in any suitable manner. Operating arm 51 and movable contact arm 54 are disposed with cooperating surfaces adjacent each other. These adjacent surfaces are capable of relative movement with respect to each other and have a layer of highly viscous liquid disposed between them. The previously mentioned dimethylpolysiloxane at 12,500 centistokes is deemed suitable. In operation, upon the pressing of the diaphragm 57 corresponding to diaphragm 13, actuator 50, operating arm 51, the layer of viscous liquid, movable contact arm 54 andmovable contact 54 a are caused to move in unison. The operatingforce is temporarily transmitted to movable contact 54a to produce this unified movement by actuator 50, operating arm 51, movable contact arm54 and the viscous liquid which comprises a force transmitting means, the viscous liquid joining the operating arm and the movable contact arm together by adhesion. The operating force in this embodiment, as in the presently preferred one, is also dissipated in time because the movable contact will be returned into engagement with the stationary contact under the force of spring 55 acting against the adhesive force of the viscous liquid, notwithstanding pressure is maintained on the diaphragm so that actuator 50 together with operating arm 51 consequently cannot be restored to their original condition by the force of spring 52. I

In the FIG. embodiment, a tube 70 filled with highly viscous liquid, such as dimethylpolysiloxane at 12,500 centistokes, is employed. This is pivotally mounted at its one end in a suitable switch housing (not shown) by pivot 71. Partially immersed in the viscous liquid is movable contact arm 72 which is hingedly mounted to the other end of tube 70 by hinge pin 73. A suitable sealant (not shown) is used to prevent the loss of the viscous liquid from that end of tube 70 from which contact arm 72 emerges. Stationary contact 74 is mounted in the switch housing in any suitable manner so that movable contact 72 is normally urged into engagement therewith by spring 75. Tube 70, as well as contact arm 72, is urged toward diaphragm 77, corresponding to diaphragm 13 of the presently preferred embodiment, by spring 78 until stop 79 abuts the inner surface of the diaphragm.

In operation, pressure of diaphragm 77 causes tube and contact arm 72 to move in usison temporarily thereby separating contact arm 72 from stationary contact 74. This temporary unified motion is produced as a result of contact arm 72 being incapable of moving very rapidly through the liquid filling tube 70 owing to the high viscosity of the liquid. Tube 70, contact arm 72 and the highly viscous liquid comprise the force transmitting means of this embodiment.

The operating force in this embodiment, as in the other two, is also dissipated over a time period because contact arm 72 will return to its unactuated position in engagement with stationary contact 74 under the force of spring 75 which overcomes the tendency of the viscous liquid to prevent the passage of the arm through it. This occurs, as it is to be understood, even though pressure is maintained on diaphragm 77 and tube 70 cannot be restored to its original position by the force of spring 78.

In both of the alternate embodiments of FIG. 4 and 5, the pressure applied to the respective diaphragm, or operating member, must be at a rate which is rapid enough to prevent the movable contact from remaining in engagement with the stationary contact by virtue of its return spring force being enough to overcome the force transmitted through the viscous liquid. Thus, in these embodiments, as in the presently preferred one, the pressure applied must be at a rate which is effective having regard to the characteristics of the force transmitting means to enable that means to transmit a temporary operating force generated by said pressure to the movable contact to move that contact out of engagement with the fixed, or stationary, contact. Also, upon the dissipation of the operating force in both alternate embodiments, as has been explained, both, like the presently preferred one, are also capable of again being operated upon the application of sufficient pressure to the operating member at an effective rate, notwithstanding the member has not been restored to its original condition.

Various modifications in the foregoing are possible. Liquids of different compositions and different viscosities than that disclosed are believed suitable although it is expected that they would change the time it takes the movable contact to return to its closed position after operation.

Other modifications will present themselves to those skilled in the art upon acquainting themselves with this disclosure. The foregoing, therefore, is to be considered illustrative and not limiting in any regard. I

What is claimed is:

l. A manually operable switch comprising a switch housing having a fixed contact mounted in said housing, a spring loaded movable contact also mounted in said housing and urged by spring force into a closed position in which the movable and fixed contacts are in engagement, an operating member suitable to have the finger of a person desiring to operate said switch pressed against it, and force transmitting means including a liquid element as its operating medium'disposed in said housing, said means being in contact with said operating member and said movable contact and responsive to a predetermined amount of pressure applied to said operating member at a rate which is effective having regard to the characteristics of said force transmitting means whereby said means transmits through said liquid medium a temporary operating force generated by said pressure to said movable contact to operate said switch to move said movable contact against the opposing spring force from said closed position to an open one in which said movable contact is out of engagement with said fixed contact, said temporary operating force being dissipated sufficiently after'said operation so that said spring force is enabled to restore said movable contact to said closed position regardless of said predetermined amount of pressure continuing to be applied to said operating member whereby said switch is again capable of operation in response to additional pressure applied at an effective rate.

2. A manually operable switch according to claim 1, in which said operating member is a flexible diaphragm, said switch housing includes a hollow cylindrical portion sealed at one end by said flexible diaphragm and said force transmitting means includes a separator which divides said hollow cylindrical portion into an actuating chamber and a dissipating chamber, one wall of said actuating chamber being formed by said flexible diaphragm, said liquid medium substantially filling each said chamber, and an aperture in said separator permitting saidliquid to flow from said actuating chamber into saiddissipating chamber, said movable contact being disposed in its closed position to close said aperture substantially, said liquid moving said movable contact from said closed to said open position while flowing from said actuating chamber into said dissipating chamber in response to said predetermined amount of pressure applied to said flexible diaphragm at said effective rate.

3. A manually operable switch according to claim 2, in which said force transmitting means also includes an elastomeric seal which forms one wall of said dissipating chamber and seals said chamber against the escape of liquid therefrom, said seal expanding outwardly upon the flow of liquid from said actuating chamber into said dissipating chamber ,to permit said dissipating chamber to receive the liquid forced through said aperture by inward flexure of said diaphragm.

4. A manually operable switch according to claim 3, in which said aperture and said movable contact when in its closed position form bleed ports which permit gradual flow of said liquid in either direction between said actuating chamber and said dissipating chamber.

5. A manually operable switch according to claim 4, in which said liquid has a dielectric constant greater than air and a viscosity of approximately 12,500 centistokes.

6. A manually operable switch according to claim 5, in which said movable contact comprises a strip of beryllium copper which is flexed into engagement with said fixed contact and thereby is maintained urged in the closed position.

7. A manually operable switch comprising a plastic body with a hollow cylindrical portion sealed at one end by a flexible diaphragm which forms one wall of said body, a separator in said cylindrical portion dividing it into a, front and rear chamber, said flexible diaphragm forming one wall of said front chamber, a liquid substantially filling both said chambers, an elastomer seal forming one wall of said rear chamber and the other end of said cylindrical portion and sealing said cylindrical portion against the escape of liquid therefrom, an aperture in said separator, a first and second electrical contact pin, one on each of two sides of said aperture, said contact pins extending through said rear chamber and said elastomer seal for ready connection in an electrical circuit, an electrical contact in said rear chamber disposed across said aperture, said contact being fixed with respect to one of said contact pins and movable with respect to the other and being sprung into engagement with the latter to be maintained urged against it by spring force, said liquid in response to an effective amount of inward flexure of said diaphragm being forced from said front chamber through said aperture into said rear chamber and in so doing moving said contact out of engagement with said latter mentioned contact pin against said opposing spring force, said elastomer seal expanding outwardly to permit said rear chamber to receive the liquid forced thereinto, said spring force restoring said contact into engagement with said latter mentioned contact pin as the pressure on the liquid in said front and rear chambers approaches equilibrium regardless of said diaphragm remaining inwardly flexed whereby said switch is again capable of operation in response to additional inward flexure of said diaphragm.

8. A manually operable switch according to claim 1, wherein said force transmitting means includes an operating arm movable in response to pressure applied to said operating means, and a contact arm upon which said movable contact is mounted, one surface of said operating arm being disposed adjacent a cooperating surface of said movable contact arm, said operating arm and said movable contact arm being mounted in said housing with said adjacent surfaces capable of relative movement, a layer of said liquid medium being disposed between the adjacent surfaces of said operating arm'and said movable contact arm, said liquid having a viscosity which is high enough to be effective to adhere said movable contact arm temporarily to said operating arm to cause said movable contact to move to said open position in response to the application to said operating means of said predetermined amount of pressure at said effective rate.

9. A manually operable switch according to claim 8, including a spring engaging said operating arm and said contact arm and applying said spring force which restores said movable contact to said closed position after a period in said open position.

10. A manually operable switch according to claim 1, wherein said force transmitting means includes a tube closed at one end hingedly mounted in said housing at said closed end and movable in response to pressure applied to said operating means, said liquid medium filling said tube, a contact arm upon which said movable contact is mounted at one end, the other end of said arm being inserted into said tube substantially the full length thereof and immersed in said liquid, said arm being pivotally mounted to said tube approximately at the open end thereof, a seal sealing said open end of said tube to said movable contact arm to prevent the escape of liquid therefrom, said liquid having a viscosity which is high enough to be effective to cause said movable contact arm to move temporarily substantially in unison with said tube upon the application to said operating means of said predetermined amount of pressure at said effective rate.

11. A manually operable switch according to claim 10, including a spring engaging said movable contact arm and applying said spring force which restores said arm to said closed position after a period in said open position. 

1. A manually operable switch comprising a switch housing having a fixed contact mounted in said housing, a spring loaded movable contact also mounted in said housing and urged by spring force into a closed position in which the movable and fixed contacts are in engagement, an operating member suitable to have the finger of a person desiring to operate said switch pressed against it, and force transmitting means including a liquid element as its operating medium disposed in said housing, said means being in contact with said operating member and said movable contact and responsive to a predetermined amount of pressure applied to said operating member at a rate which is effective having regard to the characteristics of said force transmitting means whereby said means transmits through said liquid medium a temporary operating force generated by said pressure to said movable contact to operate said switch to move said movable contact against the opposing spring force from said closed position to an open one in which said movable contact is out of engagement with said fixed contact, said temporary operating force being dissipated sufficiently after said operation so that said spring force is enabled to restore said movable contact to said closed position regardless of said predetermined amount of pressure continuing to be applied to said operating member whereby said switch is again capable of operation in response to additional pressure applied at an effective rate.
 2. A manually operable switch according to claim 1, in which said operating member is a flexible diaphragm, said switch housing includes a hollow cylindrical portion sealed at one end by said flexible diaphragm and said force transmitting means includes a separator which divides said hollow cylindrical portion into an actuating chamber and a dissipating chamber, one wall of said actuating chamber being formed by said flexible diaphragm, said liquid medium substantially filling each said chamber, and an aperture in said separator permitting said liquid to flow from said actuating chamber into said dissipating chamber, said movable contact being disposed in its closed position to close said aperture substantially, said liquid moving said movable contact from said closed to said open position while flowing from said actuating chamber into said dissipating chamber in response to said predetermined amount of pressure applied to said flexible diaphragm at said effective rate.
 3. A manually operable switch according to claim 2, in which said force transmitting means also includes an elastomeric seal which forms one wall of said dissipating chamber and seals said chamber against the escape of liquid therefrom, Said seal expanding outwardly upon the flow of liquid from said actuating chamber into said dissipating chamber to permit said dissipating chamber to receive the liquid forced through said aperture by inward flexure of said diaphragm.
 4. A manually operable switch according to claim 3, in which said aperture and said movable contact when in its closed position form bleed ports which permit gradual flow of said liquid in either direction between said actuating chamber and said dissipating chamber.
 5. A manually operable switch according to claim 4, in which said liquid has a dielectric constant greater than air and a viscosity of approximately 12,500 centistokes.
 6. A manually operable switch according to claim 5, in which said movable contact comprises a strip of beryllium copper which is flexed into engagement with said fixed contact and thereby is maintained urged in the closed position.
 7. A manually operable switch comprising a plastic body with a hollow cylindrical portion sealed at one end by a flexible diaphragm which forms one wall of said body, a separator in said cylindrical portion dividing it into a front and rear chamber, said flexible diaphragm forming one wall of said front chamber, a liquid substantially filling both said chambers, an elastomer seal forming one wall of said rear chamber and the other end of said cylindrical portion and sealing said cylindrical portion against the escape of liquid therefrom, an aperture in said separator, a first and second electrical contact pin, one on each of two sides of said aperture, said contact pins extending through said rear chamber and said elastomer seal for ready connection in an electrical circuit, an electrical contact in said rear chamber disposed across said aperture, said contact being fixed with respect to one of said contact pins and movable with respect to the other and being sprung into engagement with the latter to be maintained urged against it by spring force, said liquid in response to an effective amount of inward flexure of said diaphragm being forced from said front chamber through said aperture into said rear chamber and in so doing moving said contact out of engagement with said latter mentioned contact pin against said opposing spring force, said elastomer seal expanding outwardly to permit said rear chamber to receive the liquid forced thereinto, said spring force restoring said contact into engagement with said latter mentioned contact pin as the pressure on the liquid in said front and rear chambers approaches equilibrium regardless of said diaphragm remaining inwardly flexed whereby said switch is again capable of operation in response to additional inward flexure of said diaphragm.
 8. A manually operable switch according to claim 1, wherein said force transmitting means includes an operating arm movable in response to pressure applied to said operating means, and a contact arm upon which said movable contact is mounted, one surface of said operating arm being disposed adjacent a cooperating surface of said movable contact arm, said operating arm and said movable contact arm being mounted in said housing with said adjacent surfaces capable of relative movement, a layer of said liquid medium being disposed between the adjacent surfaces of said operating arm and said movable contact arm, said liquid having a viscosity which is high enough to be effective to adhere said movable contact arm temporarily to said operating arm to cause said movable contact to move to said open position in response to the application to said operating means of said predetermined amount of pressure at said effective rate.
 9. A manually operable switch according to claim 8, including a spring engaging said operating arm and said contact arm and applying said spring force which restores said movable contact to said closed position after a period in said open position.
 10. A manually operable switch according to claim 1, wherein said force transmitting means includes a tube closed at one end hingedly mounted in said housing at said closed end and movable in response to pressure applied to said operating means, said liquid medium filling said tube, a contact arm upon which said movable contact is mounted at one end, the other end of said arm being inserted into said tube substantially the full length thereof and immersed in said liquid, said arm being pivotally mounted to said tube approximately at the open end thereof, a seal sealing said open end of said tube to said movable contact arm to prevent the escape of liquid therefrom, said liquid having a viscosity which is high enough to be effective to cause said movable contact arm to move temporarily substantially in unison with said tube upon the application to said operating means of said predetermined amount of pressure at said effective rate.
 11. A manually operable switch according to claim 10, including a spring engaging said movable contact arm and applying said spring force which restores said arm to said closed position after a period in said open position. 